1. Field of the Invention
The present invention relates to a machine component composed of an oxide ceramic material which has a sealing action and is in sliding contact, such as, for example, slip rings for mechanical seals and valve discs for mixing valves, especially valve discs for sanitary water mixers.
2. Description of the Prior Art
Machine components of oxide ceramic materials are presently known. These include, for example, valve discs which are used in control elements consisting preferably of two such valve discs, such as those installed in mixing valves, and in particular, those used in mixers in the sanitary area to regulate the flow of liquid. For example, a ceramic valve seat which consists of 85-99 weight percent of aluminum oxide and 1-4 weight percent of talc, is described in German Auslegeschrift No. 12 82 377. In a preferred modification, such a valve seat contains 6 weight percent of kaolin with an appropriate reduction in the aluminum oxide content.
French Pat. No. 14 54 755 discloses the manufacture of such valve parts from mixtures which contain 35-70 weight percent of zirconium oxide as well as 7 to 30 weight percent of calcium- and zirconium silicate, 0 to 30 weight percent of magnesium- and zirconium silicate, 0 to 25 weight percent of potter's clay and 0 to 25 weight percent of kaolin.
The advantage of these known ceramic valve discs lies in their improved abrasion resistance and in the greater resistance towards erosion and corrosion relative to valve parts manufactured from hard metals. According to a further proposal such as that in German Auslegeschrift No. 12 91 957, the sealing effect of valve discs composed of 95 to 100 weight percent of aluminum oxide, 0 to 3 weight percent of talc and 0 to 3 weight percent of kaolin is improved by lapping and polishing the engaged sides of the valve discs so that they have a flatness of three light bands and a surface finish with a root mean square value (mean geometric roughness) of less than 10.
Besides these reference quantities, which characterize the quality of a ceramic machine part, such as, a valve sealing disc and a slip ring, the previously known machine components are judged by the profile bearing ratio. According to DIN 4762, the profile bearing ratio known in various technological areas in which the evaluation of surface quality plays an important role, is understood to be the ratio of the bearing length to the reference length. The manufacture of leakproof machine components being in sliding contact was previously based on achieving the necessary leakproofness by providing a high profile bearing ratio. In actual fact, a previously known valve discs and slip rings, the percentage of profile bearing length to total length is greater than 70 percent. However, as the profile bearing length to the total length increases, the force required, for example, for mutually displacing two engaged valve discs, also increases. As a result of the high profile bearing ratio, a high displacement force is therefore also required in the known valve discs.
In order to make up for the disadvantage of the high displacement force required, the art has resorted to lubricating the space between the valve discs with a grease which is usually based on silicone. The grease is initially introduced in so-called grease pockets, which are recesses in the surface of the valve discs. However, because of the effect of water, the action of the grease does not last and eventually disappears. Consequently, after this point is reached, a higher displacement force must be employed to use the device. This results in increased wear, because the impurities in the water, such as, for example, sand, increasingly damage the smooth surface of the flat valve discs, which lie on top of one another.
This is particularly disadvantageous in, for example, a sanitary mixing valve and especially an older valve. Thus, a higher displacement force makes it impossible to achieve fine control and mixing of hot and cold water flows when first attempted, and under certain circumstances, the adjustment will have to be repeatedly corrected.
Reducing the profile bearing ratio of the valve discs by grinding with a coarser grain of diamond, has also been attempted. This action also did not have the desired effect because the sealing action of the control elements falls off with the decreased proportion of structural support, e.g., less than 40%, produced in this manner. The disadvantages of previously known slip rings lie in the fact that the dry friction increases with too high a ratio of profile bearing length to total length and this creates dry operating temperatures of more than 300.degree. C.